Ovarian cancer is one of the most common causes of death due to cancer in women. Boring C. C. et. al. CA-Cancer J. Clin. 41,19-36, (1991). In about 80-90% of ovarian cancer cases, the ovarian surface epithelium is thought to be the tissue source in which the cancerous transformation occurs. Nicosia S. V. Pathology of Human Neoplasms. New York: Raven Press 435-486, (1988); Scully R. E. Am. J. Pathol. 87:686-720, (1977). The ovarian surface epithelium (OSE) is a single cell layer covering the surface of the ovary and is contiguous with coelomic mesothelium at the ovarian hilum. Dubeau L. et. al. Anticancer Research 10: 1233-1240, (1990). The OSE cells are thought to be derived from mesothelial cells covering the gonadal ridge. Mesothelial cells stromalize, migrate inside the ovary, and become granulosa cells. Granulosa cells, one of the major endocrine cell types in the ovary, first appear in a primordial follicle as a single layer of cells surrounding an oocyte during prenatal life. As each follicle becomes active, the oocyte begins to enlarge in size and granulosa cells begin to divide, increase in number, and secrete estrogen. As the follicle matures, granulosa cells stop dividing and the follicle is erupted to the oocyte in a process known as ovulation. After ovulation, the granulosa cells then differentiate into luteal cells of the developing corpus luteum from which progesterone is secreted.
The lack of human ovary tissue models makes efforts to confirm the ovarian surface epithelium as the source of cancerous growth difficult. Further, there is a lack of understanding about the development of ovarian surface epithelial cell during oogenesis and follicle formation because culturing conditions in which the OSE cells can be isolated and still retain their original characteristics are still being refined. The identification, isolation, and characterization of an ovarian precursor cell that can reliably differentiate into multiple types of cells, such as OSE cells and granulosa cells, may be important in the understanding of the biology of ovarian cells and why cancerous transformations occur like in ovarian cancer and perhaps how the transformations can be prevented. However, the ovarian precursor cells, like many precursor cells, are few in number and difficult to isolate. Once isolated, ovarian precursor cells are difficult to culture to the extent that they retain their precursor traits. It is postulated that there are precursors to granulosa cells and OSE cells, however, the work accomplished to date only isolates OSE cells and granulosa cells but not a common precursor to both types of cells.
There have been several reports of isolation and culturing methods of human OSE cells. Kruk P. A. et. al. Laboratory Investigation 63(1), 132-136, (1990); Siemens C. H. and Auersperg N. Journal of Cellular Physiology 134, 347-356, (1988); Auersperg N. et. al. In Vitro 20(10) 743-755, (1984). In these reports, human OSE cells that are isolated and cultured are already in terminally differentiated form. The isolation and characterization of OSE cells and granulosa cells in rabbits have also been reported. Piquette G. N. and Timms B. G. In Vitro Cell. Dev. Biol. 26: 471-481, (1990). However, the OSE cells are already differentiated and therefore, make studying events related to early OSE development or early cancerous transformation during OSE development difficult. Some research progress has been accomplished toward identifying precursors to granulosa cells. The number of clonal precursors of granulosa cells in mouse ovary has been determined to be small in number (about five) based on a technique of random X-chromosome inactivation and the use of an X-linked alloenzyme variant of phosphoglycerate kinase-1 (PGK-1), a variant of a glycolytic enzyme. Telfer E. et. al. J. Reprod. Fert. 84, 105-110, (1988). Other research related to ovarian granulosa stem cells demonstrate that granulosa cells, not oocytes, are the source of telomerase activity in the ovary and therefore, as the authors state, their results supports their hypothesis that granulosa cells arise from a population of stem cells. Lavranos T. C., et. al. Biol. of Reproduction 61, 358-366, (1999). One line of thought in ovarian precursor cell research advocates the use of fetal, not adult, ovaries as a source of cells because precursor cells in fetus would presumably have higher activity and be greater in number than in adults. To this end, fetal epithelial cells from a region of the ovary called rete ovarii have been described but these cells are not described as having pluripotent capacity to differentiate into any other types of ovarian mesothelial cells. Dubeau et. al. Anticancer Research 10: 1233-1240, (1990).
Accordingly, there exists a need for methods to identify, isolate, culture, and characterize ovarian mesothelial cells that have pluripotent capabilities. The invention described herein overcomes many of the aforementioned shortcomings and also provides related advantages.